Modulation



moswos Dec. 31, 1935.

MODULATION 2 Sheets-Shet 1 Filed Dec. 14, 1931 A 6600 mxsm 5* 220 DEFLECT/O/VS 0F D/APHRAGM 'INVENTOR MENDEL OSNOS I BY g I ATTORNEY Dec. 31, 1935. M. osNOS 2,025,955

MODULAT I ON Filed Dec. 14, 1931 2 Sheets-Sheet 2' INVENTOR MENDEL OSNOS BY flQQ W ATTORNEY Patented Dec. 31, 1935 UNITED STATES PATENT OFFICE 2,025,955 MODULATION Application December 14, 1931, Serial No. 580,861 In Germany December 15, 1930 4 Claims.

that the non-reactive or dissipative resistance for the damping of the crystal circuit is acted upon by the voice, music, picture impulses, etc.

This idea maybe carried into practice by that in series with the crystal controlling a hot-cathode or thermionic tube, there is connected a variable resistance whose size or value is acted upon by voice or music currents or picture pulses, etc. However, particularly high sensitiveness is insured by making arrangements so that the size of the gas column consonant or co-vibrating. with the crystal controlling the tube, and consequently the damping of the crystal is influenced by the music or voice currents and the like.

It is known that the damping of a piezo-electric crystal confined inside air or some other gas is governed not only by its internal friction, but also by acoustic or super-audible mechanical radiations or is greatly dependent upon the covibrating air layer (see, for instance, article by Dr. K. Heegner entitled Measurements of piezoelectric crystals, published in No. 44 of Telefunken-Zeitung, 1926, pages et seq.)

Now, according to the present invention this variability of the acoustic damping of the crystals may be utilizd in this manner that the said damping is controlled or regulated by the voice, music, picture radiations, etc., or the current or potential variations occasioned thereby in a suitable device.

Now, in the case of separately-excited crystals the current flowing through the crystal and in self-excited crystals, 1. e., crystals excited by way of a tube associated therewith, also, the current of the thermionic tube controlled by the same depends upon the damping of the crystal. Hence, by the agency of variations of damping of a crystal caused by musical or voice currents, according to this invention, corresponding current or voltage variations are producible in suitable apparatus, and these variations may be fed, directly or in amplified form, to an additional transmitter stage or to any desired transmitter in a way well known in the prior art. This scheme insures a very effective way of transmitting the voice, music, pictures, etc.

I A more complete understanding of the invention will be had from the description thereof which follows, and therefrom when read in connection with the attached drawings throughout which like reference characters indicate like parts, and in which,

Figs. 1 and 3 show a crystal mounted adjacent 5 control means;

Fig. 2 shows the relation between the distancebetween the reflectors and the intensity of current in the crystal circuit;

Fig. 4 shows in detail a mounting for the 1 crystal;

Fig. 5 shows a circuit arrangement incorporating the present invention;

Fig. 6 shows the relationbetween current flow in the crystal and the frequency of vibration of 15 the control means; while Figs. 7, 8, and 9 show further application of the present invention.

Referring to the drawings in Fig. l, l denotes for instance, a piezo-electric crystal vibrating in 20 its longitudinal axis, the said crystal being held between the electrodes 2. The latter are connected by way of the leads 3 in the circuit to be regulated, say, in the grid circuit of a transmitter valve. Opposite the crystal, most preferably at right angles to the direction of oscillations, as indicated by the arrow, there is disposed a sound reflector 4. In this arrangement, as is well known, the current in the crystal is greatly dependent upon the distance between the reflector and the crystal as is shown in Fig. 2, the curves of which are taken from the Dr. Heegner article above quoted, where the crystal currents indicated by the ordinates, or the current proportional thereto, are plotted against the dis- 35 tance between the reflector and the crystal as indicated by the abscissa.

Fig. 2 shows that at \=6600 m, for a crystal of 5x25x60 mm. when changing the distance of the reflector from 4.2 to 4.7 mm., i. e., by 0.5 mm., the current changes from 42 to 105 galvanometer divisions, i. e., 2.5 times, the change being almost rectilinear. 1 7

According to the invention the reflector consists, for instance, of the telephone diaphragm 4 45 of Fig. 3, which is capable of small changes in the distance from the crystal I and which is so arranged and is so influenced in a way known in the art by means of an electromagnet 5 that in the state of rest, say, when no voice actions are present, the distance between diaphragm and crystal is 4.5 mm. so that the crystal current amounts to about '73 units of current, while when speaking-is going on, the maximum diaphragm deflections are} equal to or less than 0.25.

In the case of a transversally oscillating crystal (see Fig. 4), according to another object of the invention, one of the electrodes, say, the upper one as indicated at 6, may be made elastic or in ,the shape of a telephone diaphragm such as 4 in Fig. 3.

The sensitiveness with which the crystal responds to changes in the reflector distance, in the form of current variations is markedly dependent upon its natural period or wave. The smaller the natural wave the higher will be its responsiveness or the slope or steepness of its current curve in dependence upon the distance separating the crystals and the reflector.

For example, in some more recent research made 011 a crystal-controlled vacuum tube connected in a way as shown in Fig. 5, and a crystal whose natural period or wave was 117 meters, with the distance of its electrode 2 being adjusted by the aid of a micrometer screw 9, there was found a graph giving the interdependence of the current. i and the distance between the crystal and its electrode or the setting angle of the micrometer of a shape as shown in Fig. 6. This graph demonstrates that, for instance, in the branch P P2, there happens a change in the current flowfrom zero to 70 units of deflections or divisions upon changing the position of the micrometer screw of the electrode by only 1 degree corresponding to a shift of the electrode by only 2.5 x 10- mm.

Hence, if extreme sensitivity is desired, ar-

rangements for this crystal will have to be made so that in the state of rest, i. e., when no talking or sound actions take place, the distance between crystal and the diaphragm corresponds to a current of 2', equal to or greater than 120 preferably greater, to thereby improve the stability of operation.

In this manner it is empirically or experimentally feasible to ascertain the optimum current slope or steepness for every and any crystal and on this basis the mean distance between the diaphragm and the crystal, i. e., when the diaphragm is at rest, is determinable and may be conveniently chosen.

One particular fact that may be taken from the graph of Fig. 6 is that the deflections or swings of the diaphragm while being acted upon by the voice, should not assume undue proportions, lest the current is liable to suddenly change or leap to another branch of the curve, and this would mean voice distortion.

If the sensitiveness of the crystal is high, one

. of the electrodes, say, the upper one indicated at (Fig. '7) may beacted upon directed through a horn by means of the sound waves produced by the voice or music, etc.

The scheme in Fig. 7 in addition comprises an amplifier tube 8 with a leak resistance I I, an inductance coil l2, a plate oscillation circuit l3, a compensating condenser M, a blocking condenser l5 and an audio frequency transformer Tr shunted by a condenser N5, the secondary winding thereof furnishing amplified voice or music currents. The micrometer screw ll serves for the adjustment of the mean distance between the crystal I and the mobile electrode 6.

The mobile electrode of the crystal may be influenced in the fashion of a telephone diaphragm by the aid of microphone currents. This scheme is shown, for instance, in Fig. 8. From the microphone M leads 3 are brought to the magnet 5 which moves the diaphragm 4 at the rhythm of voice or music currents, the position of rest or inoperation of the diaphragm and its maximum deflection being chosen suitably in a way as hereinbefore described.

As a result as hereinbefore explained, there arise amplified current or voltage impulses in the output transformer'Tr of the tube 8. The arrangement of this invention serves here, as will thus be seen, as an amplifier stage between the microphone and the transformer Tr. The amplified energy of acoustic frequency derived from 10 the secondary winding of transformer Tr may be fed to another stage or to another transmitter, for instance, for the purpose of modulating oscillations of an oscillator, although the energy may also be supplied to another electromagnet 5' and to a similar arrangement as shown in Fig. 8. (See Fig. 9).

The direct current resistance of tube 8 and 8 changes at the rhythm of the voice or musical currents. As a result they may also be used in known manner as variable leaks in any desired stage of the existent transmitter.

The number of cascades or stages according to the invention is unlimited.

What may be mentioned in this connection is that the crystals .of the various stages may have widely different frequencies. Their wave-lengths are also entirely independent of the wave-length of the master transmitter.

Hence, itis possible according to this invention 1. A circuit for amplifying audible frequency signals comprising. a thermionic tube having an anode, a cathode and a control grid electrode, an inductance and a resistance connected between the control grid and cathode of said tube, a piezo electric crystal having its .impedance connected in parallel with said inductance and resistance, a parallel resonant circuit connected between said anode and said control grid, means for tuning said circuit to a frequency which is high compared with the frequency to be amplified, a connection between said parallel resonant circuit and the cathode of said tube, an audible frequency transformer having its primary winding in parallel with a portion of said connection,-and a variable gas column associated with said crystal to impede the oscillation thereof at signal frequency.

2. A cascade audible frequency amplifier comprising, a thermionic tube having its control grid and anode electrodes connected in a regeneratively coupled oscillation producing circuit tuned to a super-audible frequency, a connection between said circuit and the cathode of said tube, audible frequency coupling means connected with said connection, a piezo-electric crystal connected between the control electrode and cathode of said tube, means for varying the freedom of oscillation of said crystal at audible frequency, a second thermionic tube having an anode, a control electrode and a cathode, a crystal connected be- 7 tween the control electrode and cathode of said second named tube, an electro-mechanical coupling between said audible frequency coupling means and an electrode of said crystal, a superaudible frequency oscillation producing circuit 7 connected between the anode and control electrode of said second named tube, means for connecting a point on said super-audible frequency oscillation circuit to the cathode of said second named tube,- and audible frequency coupling means connected with said last named connection. 1

3. An audible frequency amplifier comprising, a thermionic tube having an anode, a cathode and a control electrode, an above audible frequency oscillation circuit comprising inductance and capacity connected between said control electrode and said anode, means for completing the above audible circuit between said anode and said cathode and said control electrode and said cathode comprising, a capacity connecting a point on the inductance in said super-audible circuit to the cathode of said tube, an audible frequency output transformer having its primary winding connected in parallel with said capacity, an inductance and a resistance connected between the control electrode and cathode of said tube, a piezoelectric crystal connected in parallel with said inductance and said resistance, and means for damping the tendency of said crystal to oscillate, said means operating at the frequency to be amplified.

4. A circuit for amplifying audible frequency signals comprising, a thermionic tube having a vitreous closure member enclosing electrodes including an anode, a cathode and a control grid, a frequency determining circuit including a piezoelectric crystal connected with the control grid of said tube, the frequency of said circuit being above the frequency of the signals to be amplified, a circuit normally resonant at a frequency above the frequency of the signals to be amplified connected between the anode and cathode of said tube, said circuit including a reactance, an audible frequency coupling device connected with said reactance to couple the same to a load circuit, and a variable air column in which said crystal is positioned for varying the damping of 20 said crystal at signal frequency.

MENDEL OSNOS. 

